Plyometric exercise is a major tool for improving explosive actions. This study aimed to compare the efficacy of a vertical and horizontal plyometric training program on stretch-shortening performance variables in adolescent soccer players. Thirty-two male soccer players (aged 12.09 ± 0.89 years, with soccer experience 5.37 ± 1.58 years) were divided into horizontal plyometric, vertical plyometric, or control groups. The horizontal and vertical plyometric groups participated in a 6-week training program that was performed twice per week, with a 48-h interval, in conjunction with regular soccer training. The control group participated only in regular soccer training. Vertical jump height, reactive strength index, leg stiffness, ground contact time, standing long jump distance, agility, and 10 and 20 m sprint performances were tested as stretch-shortening performance variables of the participants. Stretch-shortening performance variables were assessed before and after completion of the training program. The results showed that either horizontal or vertical plyometric training had no effect on VJH, RSI, GCT, or Kleg performance (F = 2.14, 1.32, 0.66, 1.03; p > 0.05). Furthermore, there was no effect on SLJ, 10 m sprint, 20 m sprint, or agility performance (F = 2.06, 0.14, 0.06, 0.27; p > 0.05). A 6-week horizontal or vertical plyometric intervention was found to be insufficient to elicit stretch-shortening performance enhancement in adolescent male soccer players. Although there was no performance change in any group, it was observed that the players enjoyed plyometric training. Therefore, coaches could safely use plyometric exercises to design enjoyable training programs.
Keywords: adolescent players; plyometric; soccer; stretch-shortening cycle.